Background: We assessed the outcome and prognostic factors in men with prostate cancer after luteinizing hormone-releasing hormone agonist monotherapy. Methods: Between April 1998 and August 2002, 62 men with prostate cancer who were treated with monotherapy at our institution were included in this analysis. Prostate-specific antigen (PSA) failure-free (bNED) survival was calculated using Kaplan-Meier methods. Prognostic factors were evaluated using Cox proportional hazards regression model. Results: We reviewed the data of patients, with a median follow-up from the commencement of monotherapy of 26 months. The overall survival rate at 3 years was 89.9%. The bNED survival rate was 63.7% at 3 years. Of the 20 patients with clinical stage B, 2 progressed to PSA failure, whereas PSA failure was seen in 8 of 30 patients with stage C and 8 of 12 patients with stage D. The significant factors for bNED status were an initial PSA level of <30 ng/ml (p=0.0044), achievement of PSA nadir level of <2.0 ng/ml (p<0.001), and Gleason score of ≤6 (p<0.001). Conclusions: Patients with high clinical stage, a high initial PSA level of ≥30 ng/ml, and high Gleason score of ≥7 are at increased risk for PSA failure. Failure to achieve PSA nadir level of <2.0 ng/ml is an important predictor of the progression. The use of PSA nadir can provide useful guidelines for the reconsideration of treatment in patients who have received monotherapy.